Storage vessels, and particularly aircraft fuel tanks, must be free of leaks, even microscopic ones, to insure their integrity for operation under harsh environments. In order to test the integrity of vessels/tanks alter manufacture, or after use once put in service, leak detection systems are used. Typically these have a long hose attached to a vacuum pump to pull in a sample of gas and air. The hose terminates in a defined-size metal tube terminating in a sniffer probe that functions as an inlet nozzle. The vessel/tank to be tested is pressurized with a selected mix of air and helium. Then the sniffer probe is guided over all surfaces and outlet valves and lines of the tank to draw in samples of gas, in the ease of a sound tank, having no leaks, ambient air, but in the ease of a leaking tank, helium-laden air.
The probe sample is routed to a helium sensor which detects the helium and can convert the detection signal into a quantitative rate of leak. These helium sensors are relatively conventional, one type working by ionizing a gas sample containing helium, passing the ionized sample through a magnetic field and collecting the helium ions as they emerge to produce an electric current which is used to drive an ammeter the values of which are converted to quantitative leak rates. Another system rises a membrane, which allows only Helium to pass through for detection.
A serious problem is presented by currently available helium leak detections systems in that the hose line from the sensor to the probe tip is required to be on the order of 10-50 feet in length to permit the detection technician to climb up on aircraft wings to reach tanks that are in service. A typical response time for a 10 foot snifter hose is around 10 seconds, since it takes that long for a sniffed sample to be delivered to the helium sensor. By that time the technician may have moved on to a different area of the tank, so that an alarm means that the technician must return to a previous area in order to pin-point the leak location.
In addition, many tanks under test are located in hazardous environments, such as Class 1, Division 1, Group D hazardous environments, such as those involving volatile organic fuels or solvents. Accordingly, the electrical equipment associated with the probe pump, sensor, control system and alarm system cannot be used in such environments. In order to service in such environments, present systems require even longer hoses, or sequestration of the pump, sensor and associated electrical systems in separate rooms.
Accordingly, there is a significant, unmet need to have a faster response time in helium leak detection so that retracing a sampling path is not required, and permits operating, portably, in hazardous environments.